Smartcard technology is directed to structures with embedded integrated circuit units. Smartcards can be contact-based (e.g., conforming to ISO/IEC 7810 and ISO/IEC 7816), contactless (e.g., Radio-Frequency Identification (RFID) card), or a dual-interface (e.g., both contact-based and contactless). RFID technology is directed to wireless communication between one object, typically referred to as a RFID tag, and another object, typically referred to as a RFID reader/writer. RFID technology, and smartcard technology in general, has been adopted, and is increasingly being used, in virtually every industry, including, for example, manufacturing, transportation, retail, and waste management.
Laminated smartcards (contact-based or contactless), tickets and passports are typically made by sandwiching layers of plastic together. At the inner most layer is an RFID antenna assembly structure, which can be made by embedding wires into a plastic sheet, printing an antenna using conductive ink onto a plastic sheet, and/or etching a copper or aluminum clad sheet of plastic to create a conductive trace as an antenna. An integrated circuit unit (including, e.g., a semiconductor chip) is coupled to the antenna assembly structure. The integrated circuit can include, for example, a complex microprocessor for a smartcard or a passport, or a more simple circuit for a building access card or ticket.
FIG. 1 is a cross-sectional view of an exemplary laminated structure according to the prior art. Layer 5 is an antenna substrate that supports an antenna assembly and an integrated circuit unit 6. Layer 4 is a bonding material used to adhere the antenna substrate to Layer 3. Layer 3 is a white core PVC with heat seal coating HS-26 or similar seal coating. Layer 2 is a white core PVC front-side layer that can include print information. Layer 1 is a PVC overlay with a standard heat seal and/or protective coating. Between the antenna assembly/IC unit and the layers, air gaps 7 can form given the antenna and IC unit components and resultant non-uniformity of the antenna substrate.
When such gaps (or empty spaces) are present in the laminated structure, for example, being caused by the chip recess and/or the conductors (e.g., antenna tracks) on the antenna assembly, these gaps or spaces can cause small undulations on the surface of the laminated structure. Such artifacts are considered undesirable and detract from the quality of the card. In addition, thermal printing processes typically require an extremely flat surface to make uniform colors. If the surface is not flat, a blemish can be seen on a card after printing.